Advanced Placement (AP) Biology Practice Exam

What do light-dependent reactions primarily produce?

1. Glucose and Oxygen

2. ATP and NADPH

3. Carbon Dioxide and Water

4. ATP and Glucose

The correct answer is: ATP and NADPH

The light-dependent reactions of photosynthesis primarily take place in the thylakoid membranes of chloroplasts and serve to capture and convert sunlight into chemical energy. During these reactions, light energy is absorbed by chlorophyll and other pigments, leading to the generation of ATP and NADPH. ATP is produced through a process called photophosphorylation, where the energy from light is used to add a phosphate group to ADP, resulting in ATP. NADPH is generated when electrons are excited by light energy and transferred through the electron transport chain, ultimately reducing NADP+ to NADPH. Both ATP and NADPH are essential energy carriers used in the subsequent light-independent reactions (Calvin cycle) to synthesize glucose and other organic molecules. The other options misrepresent the primary outputs of these initial photosynthetic reactions. While glucose and oxygen are products of photosynthesis, they are primarily formed during the Calvin cycle rather than during the light-dependent reactions. Carbon dioxide and water are reactants in the overall photosynthetic process, but they are not the products of these light-driven processes. Glucose production also occurs later in the cycle and is linked to ATP’s and NADPH's utility in synthesizing carbohydrates. Thus, B accurately captures the main products